1. Field of the Invention
The present invention generally relates to a developing apparatus and an imaging apparatus having the developing apparatus. More specifically, the present invention relates to an apparatus that develops an electrostatic latent image using a two-component developer containing a toner and a carrier.
2. Background Information
In photocopying machines, printers, fax machines, and other imaging devices, for example, an electrostatic latent image is formed by an electrophotographic method in which a uniformly charged photoreceptor drum is selectively exposed. Developing apparatuses in which toner is used to develop the electrostatic latent image are well known. A two-component developer containing a toner and a carrier is often used as the developer in such developing apparatuses. The two-component developer is affixed to a peripheral surface of a developing roller, and transferred to an electrostatic latent image formed on a peripheral surface of the photoreceptor drum, for example.
A prescribed bias voltage is applied to the developing roller in order to control the amount of toner that is transferred. A superimposed voltage having DC and AC voltage is used as the bias voltage.
A bias voltage in which a DC and AC voltage are superimposed as described above is used in an imaging apparatus disclosed in Japanese Laid-open Patent Application No. 2003-295567. A method that progressively increases the amplitude component of the AC voltage is disclosed whereby the amplitude component of the AC voltage is set to 1100 Vpp when the first to the 100,000th image are created, and to 1500 Vpp when the image count is above 100,000. Such a structure, however, lends itself to fogging and other problems. As used herein, “fogging” refers to minute amounts of toner that remain on paper that has been subjected to the imaging operation, even in blank regions where no image has been formed.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved a developing apparatus and an imaging apparatus having the developing apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.